Human phonation is driven by airflow from the lung. The larynx serves as an energy converter, transferring aerodynamic energy into acoustical energy. Aerodynamic parameters provide a practical assessment for laryngeal function during phonation. Traditional aerodynamic measurement technologies have many limitations. Specifically, measuring airflow after the vocal tract does not represent the driving parameters such as subglottal pressure. Recent progress in research suggests new parameters such as phonation threshold pressure (PTP) and vocal efficiency are essential to represent laryngeal function because they take into account both aerodynamic and acoustic energy forms. A non-invasive aerodynamic measurement system based on flow interruption technology is needed to assess laryngeal function, pathologies, and evaluate the effects of treatment. This proposal focuses on applying current aerodynamic theories and computerized instrumentation to improve methods of assessing laryngeal function. Specifically, we hope this novel system can assess subglottal pressure (SGP), vocal efficiency (VE), AC/DC ratio of glottal flow, and phonation threshold pressure (PTP). New parameters, phonation threshold flow (PTF) and phonation threshold power (PTPw), will also be investigated. The study has two interrelated parts. In part I, research will focus on developing a better airflow interruption system with computer aided design. Using an acoustically adapted model and a Finite Element Analysis (FEA) model, we will quantitatively describe the aerodynamics of the measurement system, such as the sound projection and the pressure and flow fields during and after airflow interruption. Computer modeling will help design and optimize the effects of the dimensions and shape of the measurement system. Research will focus on issues in adapting the designed system to human subjects. The measurement accuracy and comfort of various masks and mouthpieces will be investigated. The effects of audio-laryngeal reflexes will be determined, and then reduced by masking the subjects'audio feedback. A partial airflow interruption system will be developed which will not cease phonation;therefore, the measurements will be taken during phonation, as opposed to complete interruption systems that take measurements just after phonation stops. In part II, the improved measurement system developed in part I will be used to measure the laryngeal function of patients with vocal nodules and polyps, vocal fold paralysis, laryngeal carcinoma, and Parkinson's disease. The sensitivity and specificity of distinguishing normal from pathologic voices using aerodynamic parameters will be assessed based on the received operating characteristic (ROC) analysis. Aerodynamic parameters will also be measured before and after treatment to evaluate treatment effectiveness.